It has been shown that separating nonhuman primates from their mothers for a short period of time as infants results in permanent alterations in the immune system. What has not been determined is whether immune changes due to this stressor result in increased risk for morbidity or mortality. In this study we are evaluating disease progression following inoculation with SIVe660 in 20 four-year-old pigtailed macaques (Macaca nemestrina). The subjects were part of an experimental protocol at the University of Colorado, where their behavioral and immune development was closely monitored since infancy. Half of the subjects experienced a two-week maternal separation at six months of age and half did not. To date seven monkeys have been shipped to Seattle for SIV inoculation. One subject has been infected for 28 weeks and four have been infected for 8 weeks. Two additional animals are currently undergoing quarantine and will be infected in March. Blood draws taken in Seatt le b efore infection showed that animals that undergwent separation had higher proportions of suppressor/cytotoxic T lympocytes (CD8+) and natural killer cells (CD16+) than controls. They also had higher hematocrit and hemoglobin levels. In the 8 weeks after infection proportions of CD8+ cells increased for all subjects while proportions of CD4+ (Helper T lymphocytes) and CD20+ (nonactivated B lymphocytes) decreased significantly. Subjects are being tested weekly on the amount of consumption of a preferred liquid (Kool Aid). All subjects showed a significant increase in consumption in the first 8 weeks of infection; there was no difference between animals that had experienced separation and those that had not in the amount of liquid consumed. Behavioral observations are also conducted three times per week to determine behavioral changes due to infection. FUNDING NIH grant RR00166 and NIMH grants MH37373, MH19514, MH45045, and MH15442.